The present application relates to a battery pack including a nonaqueous electrolyte secondary battery having an end face from which a positive electrode terminal and a negative electrode terminal are led out, the secondary battery being received in an exterior casing, and relates to a battery-pack exterior casing receiving the nonaqueous electrolyte secondary battery.
A battery pack used in a mobile phone includes a nonaqueous electrolyte secondary battery and an exterior casing. The nonaqueous electrolyte secondary battery includes a substantially thin-plate-shaped battery element covered with a laminated sheet such that a positive electrode terminal and a negative electrode terminal are exposed. The nonaqueous electrolyte secondary battery 11 has an end face from which the positive and negative electrode terminals are let out. The exterior casing receives the nonaqueous electrolyte secondary battery and permits the positive and negative electrode terminals to be exposed.
The battery element includes a strip positive electrode, a strip negative electrode, a separator interposed between the positive and negative electrodes, the positive electrode terminal provided for the positive electrode, and the negative electrode terminal provided for the negative electrode. The positive electrode includes a positive-electrode active material layer and a positive electrode collector such that the layer is coated with the collector. The negative electrode includes a negative-electrode active material layer and a negative electrode collector such that the layer is coated with the collector.
The strip positive and negative electrodes and the separator are wound about the line extending along the direction along the widths of the electrodes and the separator, thus constituting the battery element.
The positive-electrode active material layer coated with the positive electrode collector is a mixture of a positive-electrode active material, a conductive agent, and a binder.
The negative-electrode active material coated with the negative electrode collector is a mixture of a negative-electrode active material, a conductive agent, and a binder.
The exterior casing is a resin box which receives the nonaqueous electrolyte secondary battery and permits the positive- and negative electrode terminals to be exposed.
The nonaqueous electrolyte secondary battery is received in the exterior casing, thus constructing the battery pack.
Recently, a polymer battery pack including a metal exterior casing for improvement of resistance to an externally applied shock and reduction in thickness has been used. For example, Japanese Unexamined Patent Application Publication No. 2007-184241 discloses such a polymer battery pack.
As disclosed in Japanese Unexamined Patent Application Publication No. 2007-184241, the battery pack includes a member, serving as an exterior casing, that covers two faces of a nonaqueous electrolyte secondary battery perpendicular to the direction along the thickness thereof, and further includes two members engaged in the exterior casing so as to serve as two end faces of the casing. Disadvantageously, therefore, a space for receiving a battery element in the battery pack is restricted, leading to low volume efficiency. In addition, the number of parts is large.
The battery pack disclosed in Japanese Unexamined Patent Application Publication No. 2007-184241 has the following structural problem: Since the two members, serving as the respective end faces, are engaged in the exterior casing, engagement parts prevent an increase in volume efficiency.